CN2588390Y - Etching diffracting grating wave division multiplexer - Google Patents

Abstract

The utility model belongs to an etching diffracting grating wave division multiplexer which comprises an input waveguide, an output waveguide array, a free transmission area and an etching concave grating. The utility model is characterized in that a strong-limitation tapered waveguide composed of a trapezoidal waveguide and a wedged cavity is arranged between the input waveguide and the free transmission area, the wedged cavity is positioned outside the trapezoidal waveguide, and the trapezoidal waveguide is communicated with the input waveguide. Compared with the prior art, since the strong-limitation tapered waveguide is arranged between the input waveguide and the free transmission area, the strong-limitation tapered waveguide of the utility model can provide a bridge for the slow transition from a single mode to multiple modes. In the transition process from the single mode to the multiple modes, the energy distribution of a light field gradually changes to that the peak value of the light intensity is dispersed to both sides from that the center is maximal to form a mode field shape of which the center is concave and favorable for the flatness of frequency spectrum. The device can realize the frequency spectrum performance suitable for communication application under the condition that the processes are not increased.

Description

Etching diffraction grating wavelength division multiplexer

Technical field

The invention belongs to optical communication wavelength-division multiplex field, the integrated-type plane wave division multiplexing device that particularly a kind of spectral performance is good, manufacture craft is easy.

Technical background

Optical fiber communication obtains huge development at short many decades, and sharply expand recent years especially, and nowadays optical fiber has been routed to the every nook and cranny in the world.To a great extent, optical fiber has remedied the deficiency of cable communication, and message capacity and quality are increased greatly.Yet along with The development in society and economy, people are exponential increase to the demand of information, communication service also from phone, data to broadband business developments such as video, multimedias, the bandwidth of traditional light transmission is also not enough.Fortunately on simple optical fiber, use wavelength-division multiplex (WDM) technology can become tens times, tens times, the increase power system capacity of hundreds of times, satisfy the demand that increases bandwidth.

Multiplexer/demultiplexer in the division multiplex fibre-optic communication wave system (Multiplexer/Demultiplexer) is the device of most critical.On traditional optical transmission chain, two ends add multiplexer/demultiplexer, just may realize dilatation with lower cost.Etched diffraction grating is a kind of of plane integrated waveguide multiplexer/demultiplexer, and it utilizes semiconductor technology, can be in the dense wave division multipurpose that realizes on the very little chip more than 40 passages.

The flattened spectral response of wavelength division multiplex device is very important concerning system applies.In the world the wavelength lattice point of wavelength-division multiplex is stipulated, but actual medium wavelength on these lattice points because all factors (laser instrument instability, environmental change etc.) can produce skew, this has tolerance with regard to requiring wavelength division multiplex device to the wavelength variations in the certain limit, and being embodied on the device performance is exactly the planarization of frequency spectrum.

In order to realize the wavelength division multiplex device flattened spectral response, the main at present method that adopts is as follows:

U.S. Patent No. 5,706,377. disclosed methods are to utilize Y branch to realize flattened spectral response, and the wedge angle in the Y branch will increase the Insertion Loss of device;

Another piece of writing that M.R.Amersfoort etc. deliver is entitled as " Passband broadening ofintegrated arrayed waveguide filters using multimodeinterference couplers ", Electron.Lett., 1996,32, (5), in the article of pp.449-451, adopt multimode waveguide to realize flattened spectral response, realize different three dB bandwidth by the width of regulating MMI.Because when increasing three dB bandwidth by increasing the MMI width, also further increased device Insertion Loss, the ripple (ripple) in the bandwidth, crosstalk etc., make the deterioration that device performance is apparent in view.

U.S. Patent No. 5,926,587. disclosed methods are to utilize the method for two cascaded fiber gratings to realize flattened spectral response; One piece of delivering such as A.Rign be entitled as " Multigratingmethod for flattened spectral response wavelengthmulti/demultiplexer '; Electron.Lett.; 1997; 33; (20) adopts many gratings to realize flattened spectral responses in the article of pp.1701-1702.; One piece of delivering such as Y.P.Ho is entitled as " Flat channel-passband-wavelength multiplexingand demultiplexing devicesby multiple-Roland-circle design ", IEEE Photon.Tech.Lett., 1997,9, (3), adopt a plurality of rowland coil structures to realize flattened spectral response in the article of pp.342-344..These designs require accurately optical grating construction, are difficult for realizing, to the error sensitivity in reality processing.Simultaneously, it is inferior that energy can be distributed to other levels, and big loss induces one;

People such as M.R.Amersfoort deliver is entitled as " Phased-array wavelengthdemultiplexer with flattened wavelength response ", Electron.lett., 1994,30, (4), in the article of pp.300-302, adopt the multimode output waveguide to realize flattened spectral response, directly be connected the occasion of using with detector but this method only is suitable for Wavelength division multiplexer/demultiplexer spare.

Summary of the invention

The purpose of the invention provides a kind of simple in structure, etching diffraction grating wavelength division multiplexer that spectral performance is good.

To achieve these goals, the invention is to adopt such technical scheme to solve: it comprises input waveguide, output waveguide array, free propagation region and etching concave grating is characterized in that being provided with between described input waveguide and the free propagation region strong restriction tapered waveguide.

The invention compared with prior art owing to be provided with strong restriction tapered waveguide between input waveguide and free propagation region, can provide a slow transition bridge from the single mode to the multimode and should limit the gradual change input waveguide by force.In the process of multimode transition, the light field energy distribution changes to light intensity peak by the center maximum gradually disperses to both sides at single mode, forms the mould field shape of the favourable flattened spectral response of central concave; Covering is an air on strong restriction gradual change input waveguide both sides, and its refringence is big, belongs to strong restriction waveguide on the in-plane, its steep decline in mould field distribution edge, thereby can realize better planarization effect.

Description of drawings

Fig. 1 is the structural representation of the invention

Fig. 2 is the partial structurtes synoptic diagram of the invention

Fig. 3 is the optical waveguide structure synoptic diagram of the invention

Fig. 4 is the variation of light signal field when propagating in the invention

Fig. 5 is the strong restriction gradual change input waveguide inlet end width optimal design of the invention

Fig. 6 is the strong restriction gradual change input waveguide length optimization design of the invention

Fig. 7 is the spectral response of the invention

Embodiment

With reference to accompanying drawing: the invention comprises input waveguide 1, and output waveguide array 2, free propagation region 4 and etching concave grating 5 are provided with strong restriction tapered waveguide 3 between described input waveguide 1 and the free propagation region 4; Should be made of trapezoidal waveguide and wedge shape cavity 7 by strong restriction gradual change input waveguide 3, wedge shape cavity 7 is positioned at the outside of trapezoidal waveguide, and described trapezoidal waveguide and input waveguide 1 link.

Strong restriction gradual change input waveguide 3 edges will be connected with fiber array, and spacing is adjusted to the diameter more than or equal to optical fiber.Input waveguide 1 and output waveguide 2 so only need fiber array once to aim at the same side of device, help the encapsulation of device.The light signal that comprises a plurality of wavelength enters from input waveguide 1, and light signal is before freedom of entry propagation regions 4, and the light beam of single mode will be through strong restriction gradual change input waveguide 3, and the pattern of light beam begins to change, and the distribution of light field also changes.Light field after the variation is by beginning diffusion before the strong restriction gradual change input waveguide 3 freedom of entry propagation regions 4, in free propagation region 4, propagate, light energy distribution is to each face of etching concave grating 5, the light of different wavelength accumulates in different output ports after reflecting partial wave and focusing on, and is derived by output waveguide 2.

Strong restriction gradual change input waveguide 3 is positioned at the join domain of input waveguide 1, output waveguide 2 and free transmission range 4.Input waveguide 1 and output waveguide 2 are slab waveguide, both are separated by by overlayer 6, input waveguide 1, output waveguide 2 and free propagation region 4 all have higher refractive index, and the refractive index of overlayer 6 is low slightly, and the refractive index of wedge shape cavity 7 that limits tapered waveguide 3 both sides by force is very low.At trapezoidal waveguide and two strong restriction tapered waveguides 3 that wedge shape cavity 7 constitutes, the distribution of light is transformed into the shape at two peaks by unimodal gaussian shape; The width at the two ends of trapezoidal waveguide is respectively W1 and W2, and its length is L, and its numerical value is determined by optimization method.

Strong restriction gradual change input waveguide 3 provides a slow transition bridge from the single mode to the multimode.In the process of multimode transition, the light field energy distribution changes to light intensity peak by the center maximum gradually disperses to both sides at single mode, forms the mould field shape of the favourable flattened spectral response of central concave.

Strong restriction gradual change input waveguide 3 both sides coverings are that wedge shape cavity 7 refringences are big, belong to strong restriction waveguide on the in-plane, and its steep decline in mould field distribution edge can realize better planarization effect.Because strong restriction gradual change input waveguide 3 both sides are that refractive index is 1 wedge shape cavity 7, it is the same with optical grating reflection face air afterwards, can form simultaneously on technology.

Silicon dioxide optical waveguide is one of the most frequently used material of making at present integrated optical wave guide device, follows the semiconductor fabrication process, and its technology is also the most ripe.The described basic hand of the invention forces the etched diffraction grating of gradual change input waveguide 3 structures to be produced on the planar optical waveguide material.Input waveguide 1 and output waveguide 2 are made into usually buries the type slab waveguide, and free propagation region 4 then is the strong planar waveguide of simple layer.

The strong restriction gradual change input waveguide 3 that the invention is adopted can obtain good spectral response.This structure can be used in various plane wave division multiplexing devices, comprises array waveguide grating and etched diffraction grating.The invention is more suitable in etched diffraction grating on manufacture craft.Etched diffraction grating needs two masks to do the Twi-lithography etching, limits by force in the secondary photoetching etching of can being embedded into of gradual change input waveguide 3, does not increase the complexity of technology.

Strong restriction gradual change input waveguide 3 etched diffraction grating design procedures are:

1) according to the position and the shape of definite gratings such as chromatic dispersion, Free Spectral Range, device size, ducting layer refractive index;

2) determine the position of input and output waveguide;

3) introduce strong restriction gradual change input waveguide, have two parameters to need to adjust;

4) calculate the variation of light field in the gradual change input waveguide with the light beam transmission method;

5), obtain estimating several amounts of spectral response with the spectral response of scalar diffraction theory calculating device;

6) change 3) in two parameters, repeat 4), 5) calculating; Obtain best strong restriction gradual change input waveguide design;

Here provide a design example, its parameter is as follows:

The sandwich layer refractive index	Cladding index	Centre wavelength	Free propagation zone Center Length	The order of diffraction is inferior
					1.467	?1.46	1550nm	?14mm	?16

This example is an example with the silicon dioxide optical waveguide material on the silicon base, as shown in Figure 3.Silicon dioxide optical waveguide is one of the most frequently used material of making at present integrated optical wave guide device, follows the semiconductor fabrication process, and its technology is also the most ripe.The input and output waveguide is made into usually buries the type slab waveguide, and free propagation region then is simple 3 layers of planar waveguide.In Fig. 3, silicon dioxide optical waveguide is by silicon base 8, and buffering bottom 10, cushion 6 and waveguide core layer 9 constitute, and buffering bottom 10 is positioned on the silicon base 8, and cushion 6 and waveguide core layer 9 all are arranged on the buffering bottom 10 and cushion 6 covers on the waveguide core layer 9.

With the silicon dioxide optical waveguide material on the silicon base is example, and the manufacture process of the invention is:

1) on silicon base, plates the silicon dioxide cushion of one deck than low-refraction with methods such as PECVD;

2) on the silicon dioxide cushion, plate the silicon dioxide sandwich layer of one deck high index, be used to conduct luminous energy;

3) with first mask photoetching and the shallow input and output single mode waveguide that etches on sandwich layer, be used for coupling with optical fiber;

4) plate the silicon dioxide overlayer of one deck on the sandwich layer of figure having carved than low-refraction;

5) with the photoetching and etch the diffraction grating face deeply and strong restriction gradual change input waveguide on sandwich layer of second mask;

The optimal design of strong restriction gradual change input waveguide

The mould field situation of change of strong restriction gradual change input waveguide 3 is calculated, and comparatively accurate wide-angle BPM algorithm is adopted in the invention.Under given angle, the BPM method can calculate the mould field situation of change of very long distance on the direction of propagation.In these mould fields, select to help one of planarization most, and on this position, end input waveguide, light field freedom of entry space.Fig. 4 has shown incoming wave guided mode field gradually changing on the direction of propagation.

Light field can adopt more accurate two-dimentional scalar diffraction theory to calculate in the propagation of free space and the diffraction on etched grating.The input light field to twice Diffraction Calculation of outgoing position, can get output light field to the propagation of grating and optical grating reflection.

Field distribution on the grating can be represented with following formula: $E_{\mathrm{grating}}(x^{\′},z^{\′})=\frac{1}{2}{\left(\frac{n}{\mathrm{\λ}}\right)}^{\frac{1}{2}}\underset{\mathrm{taper}}{\∫}\frac{E_{\mathrm{in}}(x,z)}{\sqrt{|{\stackrel{\mathrm{\ρ}}{r}}_g-{\stackrel{\mathrm{\ρ}}{r}}_t|}}({\cos \mathrm{\θ}}_i+{\cos \mathrm{\θ}}_d)e^{-\mathrm{ik}|{\stackrel{\mathrm{\ρ}}{r}}_g-{\stackrel{\mathrm{\ρ}}{r}}_t|}\mathrm{ds}----\left(1\right)$

Here xz is plane, etched diffraction grating place.E _InBe the normalization input field distribution of BPM algorithm computation, Be the distance of the plane of incidence to the grating flank of tooth, n and λ are effective refractive index and centre wavelength, θ _iAnd θ _dBe corresponding incident angle and angle of diffraction.Can obtain equally outgoing position (x ", the field distribution that z ") locates: $E_{\mathrm{out}}(x^{\′\′},z^{\′\′})=\frac{1}{2}{\left(\frac{n}{\mathrm{\λ}}\right)}^{\frac{1}{2}}\·\underset{\mathrm{grating}}{\∫}R\frac{E_{\mathrm{grating}}(x^{\′},z^{\′})}{\sqrt{|{\stackrel{\mathrm{\ρ}}{r}}_o-{\stackrel{\mathrm{\ρ}}{r}}_g}|}({\cos \mathrm{\θ}}_i^{\′}+{\cos \mathrm{\θ}}_d^{\′})e^{-\mathrm{ik}|{\stackrel{\mathrm{\ρ}}{r}}_o-{\stackrel{\mathrm{\ρ}}{r}}_g|}\mathrm{ds}----\left(2\right)$

Here introduced reflectivity R, corresponding integral domain, distance and angle have also changed.

For simplicity, make the input and output waveguide along the z direction, the eigenmode of single mode waveguide can be write as E _Eigen(x), the field on the output end face that calculates is E _Out(x).The luminous energy that is coupled into output waveguide is expressed as with superposition integral: $I={\left|\underset{\mathrm{output}}{\∫}{E}_{\mathrm{out}}\left(x\right){E^{*}}_{\mathrm{eigen}}\left(x\right)\mathrm{dx}\right|}^2----\left(3\right)$

Because etched diffraction grating is the linear dispersion device, the field shape that different wave length focuses on is the same, and just position linearity changes.Spectral response can be written as: $I\left(\mathrm{\λ}\right)={\left|\underset{\mathrm{output}}{\∫}{E}_{\mathrm{out}}(x-k(\mathrm{\λ}-{\mathrm{\λ}}_0)){E^{*}}_{\mathrm{eigen}}\left(x\right)\mathrm{dx}\right|}^2----\left(4\right)$

Here λ ₀Be the centre wavelength of design, k is the linear dispersion rate of grating.

In order to weigh the character of frequency spectrum, define the spectral response that quality factor comes quantitative evaluation to obtain: the ratio of three dB bandwidth and 33dB bandwidth.Quality factor approaches 1 more, and spectral performance is just good more. $Q=\frac{{\mathrm{Bandwidth}}_{3\mathrm{dB}}}{{\mathrm{Bandwidth}}_{33\mathrm{dB}}}$ The fluctuation of frequency spectrum in three dB bandwidth also is an index weighing spectral performance in addition, and this value is more for a short time to mean that light fluctuations in this scope is more little.The maximal value that this amount is defined as in interior each limit peak value of three dB bandwidth deducts minimum value.

Ripple＝Extremum _max-Extremum _min

Loss also is important index very in Passive Optical Components, the ratio of expression output spectrum maximal value and input intensity. $\mathrm{Loss}=\max \{10\log \left(\frac{P_{\mathrm{out}}}{P_{\mathrm{in}}}\right)$

Different with common device performance, we wish that loss is big relatively here, because very big often meaning of the peak value of frequency spectrum has uneven spike to exist.

In the present embodiment, the opening of having fixed tapered waveguide according to channel spacing is 16 microns.The length that changes tapered waveguide throat width and waveguide can obtain different responses.Fig. 5, Fig. 6 are to be the results of optimum design of target to strong restriction gradual change input waveguide with the quality factor in the present embodiment, and same is optimized spectral response fluctuating and loss, the tapered waveguide structure that can be optimized.The optimization result of present embodiment is: throat width is 11 microns, and tapered waveguide length is 330 microns.

Fig. 7 is the spectral response of the invention after the parameters optimization, and its three dB bandwidth is than wide a lot of with the Gaussian response among the figure, and quality factor reaches more than 0.6, and loss is about 4.6dB.

Except that above example, different waveguide materials, different tapered waveguide shapes can realize the raising of spectral response performance with the invention.The invention also can be used for other optical passive components, as array waveguide grating.

Claims (4)

1. etching diffraction grating wavelength division multiplexer, comprise input waveguide (1), output waveguide array (2), free propagation region (4) and etching concave grating (5) is characterized in that being provided with strong restriction tapered waveguide (3) between described input waveguide (1) and the free propagation region (4).

2. etching diffraction grating wavelength division multiplexer according to claim 1, it is characterized in that described strong restriction gradual change input waveguide (3) is made of trapezoidal waveguide and wedge shape cavity (7), wedge shape cavity (7) is positioned at the outside of trapezoidal waveguide, and described trapezoidal waveguide and input waveguide (1) link.

3. etching diffraction grating wavelength division multiplexer according to claim 2 is characterized in that the width at described trapezoidal waveguide two ends is respectively W1 and W2, and its length is L, and its numerical value is determined by optimization method.

4. etching diffraction grating wavelength division multiplexer according to claim 1 is characterized in that described strong restriction tapered waveguide both sides wedge shape cavities (7) and reflection grating (5) etching formation simultaneously.

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